In recent years, a polymerizable liquid crystal composition has been used in a film having optical anisotropy. A polymerizable liquid crystal composition has optical anisotropy in a liquid crystal state, and alignment of a liquid crystal compound contained is fixed through polymerization. A helical structure is induced by adding an optically active compound to a polymerizable liquid crystal compound or composition, and it is applied to various optical devices depending on the pitch of helical structure.
Examples of the application utilizing selective reflection visible light include a design purpose, such as an ornamental material, and a color filter used in a liquid crystal display device. The application thereof also includes a anticounterfeit technology since reflected light and transmitted light have peculiar metallic gloss with change in color depending on viewing angle, and such optical characteristics cannot be duplicated with an ordinary duplicator. Furthermore, owing to application of the circularly polarized light separation function, such a luminance improving film is proposed that has a structure containing a quarter-wavelength plate and an optical anisotropy film exhibiting the circularly polarized light separation function, which are laminated on a polarizing plate. In these applications, the circularly polarized light separation function is demanded to be expressed over the whole visible light region (i.e., a region having a wavelength of from 350 to 750 nm), and accordingly, plural layers having different pitches are laminated, or the pitch is changed continuously in the thickness direction of the film (as described in Y. Hisatake, et al., Asia Display/IDW '01 LCT8-2).
Examples of the application as an optical compensation film of a liquid crystal display include optical compensation in an STN (super twisted nematic) liquid crystal display (as described in JP-A-2002-6138). A film having a fixed cholesteric alignment layer that reflects an ultraviolet ray having a wavelength range of 350 nm or less is referred to as a negative C-plate. A negative C-plate is used as an optical compensation plate suitable for improving viewing angle characteristics of a display device having such a mode as VA (vertically aligned), TN (twisted nematic), OCB (optically compensated birefringence) and HAN (hybrid aligned nematic). A negative C-plate can be used for viewing angle compensation of a VA mode as a combination with an optical compensation layer exhibiting positive birefringence, such as a positive A-plate (as described in JP-A-10-153802 and JP-A-10-152782).